Evaluating Femoral-Sciatic Nerve Blocks, Epidural Analgesia, and No Use of Regional Analgesia in Dogs Undergoing Tibia-Plateau-Leveling-Osteotomy

Introduction

Cranial cruciate ligament disease and rupture are common and costly injuries in dogs.¹ Tibia-plateau-leveling-osteotomy (TPLO) is a common orthopedic procedure performed to stabilize the knee joint after ligament rupture.^2,3 TPLO is a multistep surgical procedure with numerous sources of pain stimuli including: skin incision, soft tissue dissection, arthrotomy, osteotomy, and bone plate application with screws. Thus, TPLO is a procedure that is expected to be painful. In fact, most post-surgical complications observed after surgery correlate with a painful pathophysiology, and could become the precursor for chronic pain development as has been observed in post-surgical humans.^4–7

Previous studies have described different analgesic techniques to improve pain management and outcome during TPLO surgery. In one study, epidural administration of morphine^b with bupivacaine^a provided better pain management during the first 24 hr of the post-surgical period when compared to a non-regional analgesia (NRA) group.⁴ Non-steroidal anti-inflammatory drugs have been used to help manage post-operative pain with mixed results.^8,9 Finally, the use of targeted nerve blocks has been proposed as a method for analgesia during surgical knee procedures.^10–13 A recent study comparing epidural analgesia (EA) and nerve blocks in dogs undergoing TPLO surgery showed comparable clinical results.¹⁴

In the present study, we describe retrospectively the anesthesia and analgesia characteristics after femoral-sciatic nerve blocks (FSBs) with bupivacaine^a, EA with bupivacaine^a and morphine^b, or NRA in dogs that underwent general anesthesia for unilateral TPLO surgery to correct cranial cruciate ligament disease.

The study objective was to identify potential advantages and disadvantages for each technique during TPLO surgery. One previous study compared FSB and EA prospectively eliciting comparable results between techniques.¹⁴ Our study differs in that we included a group of dogs with NRA, we included a larger number of cases, and the FSB and EA were performed by a variety of people with different skill levels in an attempt to better represent veterinary practice in small animals.

Materials and Methods

Anesthesia and medical records of dogs receiving TPLO surgery at Colorado State University Veterinary Teaching Hospital were reviewed. Dogs were included in the study if they had an easily attainable, complete, clear anesthetic record, and if they also met the inclusion criteria for one of the three groups compared. The inclusion criteria consisted of systemically healthy dogs with cranial cruciate ligament disease and dogs that underwent unilateral TPLO surgery. Dogs were included in the NRA group if they had not received any regional analgesia for TPLO surgery during anesthesia. Dogs were included in the EA group if they received an epidural injection via the lumbo-sacral space prior to TPLO surgery with bupivacaine^a and morphine^b. Dogs were included in the FSB group if they received FSBs with bupivacaine^a on the affected leg prior to TPLO surgery. Due to the retrospective approach, the anesthesia protocol was not standardized as it was determined by the anesthetist in charge of the individual case.

The epidural injections were performed by a supervised veterinary student under direct guidance a veterinary anesthesia staff member, or a veterinarian. All epidural injections were performed after the dogs were anesthetized, approximately 30–60 min prior to the start of surgery. The epidural injections were performed using a spinal needle^c. The size of the needle varied depending on the size of the dog, ranging between 20–22 gauge in diameter and 3.8–8.9 cm in length (1.5–3.5 inches). The spinal needle was inserted at the level of the lumbo-sacral space. A glass syringe was used to determine the loss of resistance, indicative of correct needle penetration into the epidural space. When the needle tip was believed to be in the epidural space, 0.1 mg/kg preservative-free morphine^b (1 mg/mL) and 0.3 mg/kg bupivacaine^a 0.75% (7.5 mg/mL) were injected (∼0.14 mL/kg). The total volume of the epidural injection was limited to 6 mL. If the calculated volume were to exceed 6 mL, the bupivacaine^a dose/volume was decreased to minimize the bupivacaine^a spread to rostral spinal dermatomes.^15,16

A supervised veterinary student under direct guidance, a veterinary anesthesia staff member, or a veterinarian performed the nerve blocks while the dogs were anesthetized approximately 30–60 min prior to the start of surgery. The femoral and sciatic nerves were identified either with a peripheral nerve locator designed for regional blocks^d or an ultrasound unit^c with an 13–6 MHz linear probe placed transversely for the femoral nerve and longitudinal for the sciatic nerve as previously described^e.¹³ The femoral nerve was located at the level of the femoral triangle, cranial to the femoral artery. The sciatic nerve was located at the level of the pelvic groove between the femoral greater trochanter and the ischiatic tuberosity. An insulated needle^f was used to stimulate the nerve electrically with the peripheral nerve locator using 1–5 mAmp of current. All insulated needles were 22 gauge in diameter and the needle length ranged between 40–100 mm (1.57–3.94 inches) depending on the size of the dog. If the ultrasound unit was used, the needle was visualized as it approached the nerve and the peripheral nerve locator was used to confirm position. When the tip of the needle approached the nerve, a motor muscle twitch was observed in the affected leg in response to the nerve locator stimulation. The peripheral nerve locator current was subsequently decreased to 0.5–2 mAmp. When the muscle twitches were observed using the lower currents, 2–4 mL bupivacaine^a 0.75% (7.5 mg/mL) was injected per nerve until the muscle twitches disappeared. The stimulation current was then increased to 5 mAmp to confirm complete anesthesia of the nerves.

Parameters from the anesthesia records reported include: body weight, anesthesia premedication received (drugs, doses, and route), anesthesia induction received (drugs and doses), analgesia-anesthesia drug continuous infusions received (drugs and dose received), use of inotropic drugs for blood pressure support, systolic blood pressure, and heart rate (HR). At the end of anesthesia and surgery, the recovery quality was scored using a subjective score system assessing the quality of recovery where 0 was poor, 1 was fair–poor, 2 was fair, 3 was good–fair, and 4 was good. A good recovery was considered calm and uneventful. A fair recovery was considered when the dog appeared slightly painful or delirium/dysphoric. A poor recovery was considered when the dog's recovery was violent and pain and/or delirium/dysphoria were considered severe.

We report SBP, HR, and isoflurane^g vaporizer^h setting concentration at 15, 85, and 145 min into surgery. At 15 min, we expected primarily soft tissue surgery and a stable plane of anesthesia. At 85 min, we expected stimulation of soft tissue, joint, and bone, and at 145 min, surgery was typically culminating and most of the surgical stimulation had been completed.

Upon recovery, all dogs received carprofenⁱ when recovering from anesthesia. Carprofen ⁱ was dosed as recommended by the manufacturer (2.2 mg/kg, SQ; followed by per os, q 12 hr).

Results

Anesthesia records from 87 dogs met the inclusion criteria for the study. Seventeen dogs were in the NRA group. The EA and FSB groups were comprised of 35 dogs each. The dog's age, breed, sex, body weight, surgery duration, and anesthesia duration are reported in Table 1. The EA group had 71% male dogs compared to the NRA and FSB groups, which had 53% and 51% male dogs, respectively. All three groups had a large variety of breeds and the distribution appeared to be similar between the groups. We did not analyze breed predisposition as previously reported for TPLO surgeries.¹⁷ No other difference was identified between groups regarding age, body weight, surgery duration, or anesthesia duration.

Table 1 Age, Sex, Body Weight, Breed, Surgery Duration, and Anesthesia Duration

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Anesthesia and Surgery

Apart from regional anesthesia, the anesthetic protocols, drugs, and doses were comparable between groups (Table 2). Isoflurane^g was the inhaled anesthetic of choice for all cases.

Table 2 Anesthesia Drugs and Average Dose Used

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No relevant difference was observed in vaporizer settings between groups at any measured point. The median isoflurane^g vaporizer^h settings at 15, 85, and 145 min into surgery for the NRA group were 1.5 (±0.2%), 1.5 (±0.2%), and 1.3 (±0.3%), respectively. For the EA group they were 1.5 (±0.2%), 1.3 (±0.2%), and 1.3 (±0.2%), respectively. For the FSB group they were 1.3 (±0.1%), 1.3 (±0.1%), and 1.3 (±0.1%), respectively (p = 0.26).

Continuous infusions of analgesics and anesthetics throughout surgery were administered. In the NRA group, 24% of the dogs received a continuous infusion rate of high fentanyl^k dose (20 μg/kg/h). In the FSB and EA groups, 9% and 17% of the dogs received a similar high fentanyl^k dose, respectively. Fentanyl ^k (10 μg/kg/h) was administered to 53%, 40%, and 46% of the dogs from the NRA, FSB, and EA groups, respectively. Low-dose fentanyl ^k (2-5 μg/kg/h) was administered to 12%, 20%, and 9% of dogs from the NRA, FSB, and EA groups, respectively. Ketamine^l (10–20 μg/kg/min) continuous infusion was administered in 29%, 9%, and 11% of the dogs from the NRA, FSB, and EA groups, respectively. Intravenous lidocaine^m via continuous infusion was administered in 18% of the dogs only in the NRA group.

During the surgery period, dogs received rescue analgesia or anesthesia when they responded by moving to surgical stimulation (Table 3). In the NRA group, 98% of the dogs received rescue analgesia. In the FSB and EA groups, 46% and 58% of the dogs received rescue analgesia or anesthesia during surgery, respectively.

Table 3 Percentage of Dogs Who Received Rescue Analgesia and Anesthesia Drugs in Response to Surgical Stimulation During Anesthesia and Surgery

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The dog's physiologic parameters were maintained between groups similarly. HR and SBP were comparable between groups at the three surgical times recorded (p=0.41 for HR and p=0.14 for SBP). At 15 min into surgery, the HR in the NRA, FSB, and EA groups was 101±19, 97±26, and 98±14 beats per min (BPM), respectively, while the SBP was 125±22, 121±25, and 119±20 mmHg, respectively. At 85 min into surgery, the HR in the NRA, FSB, and EA groups was 93±22, 90±17, and 91±14 BPM, respectively, while the SBP was 120±20, 114±14, and 119±14 mmHg, respectively. Towards the end of surgery (145 min into surgery), the HR in the NRA, FSB, and EA groups was 100±28, 93±18, and 87±16 BPM, respectively, while the SBP was 121±22, 114±12, and 117±12 mmHg, respectively. In the NRA group, 35% of the dogs received inotropic support to maintain SBP above 90–100 mmHg. In the EA and FSB groups, 40% and 37% of the dogs received inotropic support to maintain blood pressure (p=0.94). All dogs were mechanically ventilated and respiratory rate was maintained throughout anesthesia between 6 and 16 breaths per min in all groups.

Discussion

In the present study, we found that FSB is a suitable technique for regional analgesia during TPLO surgery in dogs.

A previous study suggests that EA protocols elicit better perioperative analgesia in dogs undergoing TPLO surgery when compared to NRA.⁴ A different study comparing FSB versus EA for stifle surgery in dogs showed that the analgesia and anesthesia quality were comparable intra- and postoperatively.¹⁴ In the present study, we did not notice a drastic benefit from either technique when compared to NRA, but dogs in the FSB group appeared to receive lower intraoperative rescue analgesic doses and had a better recovery quality score. An important consideration is that lower doses of drugs for EA are used to minimize motor dysfunction, but this may lead to the need for more rescue analgesia during surgery and recovery period.

The use of nerve blocks with local anesthetics to treat pain intra- and peri-operatively are becoming common in human hospitals, especially for orthopedic procedures.¹⁸ Nerve blocks have been shown to improve pain management and comfort in humans, specifically during knee surgery (for reviews, see Fischer et al., Hogan et al., and Paul et al.).^18–20 Similar to our observation, in humans, the addition of nerve blocks has been shown to improve the early postoperative period and decrease the amount of administered systemic analgesic drugs, but it may not add long-term benefits.²¹ However, a multimodal approach to pain management is strongly encouraged to improve patient outcome.^22,23

Based on our findings, the addition of nerve blocks to anesthetic protocols for knee surgery is an alternative technique to help maintain anesthesia/analgesia during surgery of the canine patient. This may decrease the potential for systemic drug-induced complications, such as bradycardia, hypotension, respiratory depression, and prolonged sedation when waking up from anesthesia. In addition, the recovery quality may be better, inducing calm recoveries, absence of motor dysfunction in the contralateral limb, and decreased epidural induced urinary retention.^14,16

An important consideration in veterinary medicine and the canine patient is that FSB will induce motor dysfunction in the affected-and-treated leg. Thus, postoperative care should be considered to minimize the potential for damage and trauma of the paralyzed limb after nerve blockade. At our hospital, the motor paralysis can be observed up to 6 hr post-block administration, and limb dysfunction with conscious proprioception deficits can be observed up to 12 hr depending on the dose and drug used for the block.

The quality of recovery was assessed at the time of endotracheal extubation from anesthesia. After TPLO surgery, it has been suggested that 20–30% of dogs will wake up with dysphoria.²⁴ In the present study, the results obtained showed a similar incidence of fair-to-poor recovery quality with the NRA group having the highest incidence of poor recoveries.

This study was limited by its retrospective nature. Multiple variables between groups were unable to be controlled, and the reasons for certain anesthetic-related decisions were unable to be confirmed. For example, we cannot determine if the anesthesia/analgesia intravenous continuous infusions or doses used were always in response to painful stimulation or if they were to prophylactically prevent pain sensation and processing during surgery. We do not know or cannot confirm what determined the isoflurane^g vaporizer^h setting throughout anesthesia. Different personnel with different skill levels performed anesthesia and surgery, but, hopefully, this effect is representative of veterinary medicine elsewhere. The propofolⁿ anesthesia induction dose varied between groups, but the high incidence of variables in the study precluded any potential conclusion. Additionally, as stated above, low morphine^b and bupivacaine^a doses were used in the EA group to avoid motor dysfunction and urine retention, which may have unfairly biased towards the FSB group. It is known that by decreasing the epidural dose the technique becomes less reliable for pain management, including during knee surgery.^25–27

In the present study, no major complications from FSB were encountered in the retrospective evaluation. The study suggests that these analgesic techniques are relatively safe. However, extreme caution is still recommended because the technique may be relatively safe only when properly performed or supervised by trained personnel.

Conclusion

In conclusion, the study shows that as part of a multimodal anesthesia/analgesia approach for TPLO surgery, the use of femoral and sciatic nerve blocks with bupivacaine^a is an alternative technique to help with analgesia and anesthesia.